In U.S. Pat. Nos. B1 5,044,852, 5,584,630 and others, fasteners are disclosed which utilize quick-setting adhesives, such as anaerobic or cyanoacrylate adhesives. The fasteners are so designed that upon pressing them against a substrate to which the fasteners are to be attached, the adhesive is automatically dispensed into the interface between the fastener and the substrate and in but moments, the fastener is securely attached to the substrate.
The adhesive is contained in a reservoir in the fastener. The reservoir is made from a material which is intended neither to react with nor promote curing of the adhesive therewithin. The remainder of the fastener is intended to bond with the adhesive as the latter cures and may be formed of a rigid plastic. Examples of suitable plastics are found in U.S. Pat. No. 5,277,530.
It has been discovered that in some instances the adhesive has tended to cure in the reservoir notwithstanding the non-reactive character of the reservoir material, particularly if the loaded reservoir in a fastener is stored for a long interval. For example, an adhesive such as a cyanoacrylate, must have atmospheric water vapor excluded if premature curing is to be prevented. On the other hand, if an anaerobic adhesive is used, oxygen must be present to prevent premature curing. Accordingly, studies of these problems have indicated that the water vapor in the ambient atmosphere is apparently captured in the reservoir at the time it is filled with the adhesive and/or the piston is inserted in the reservoir cup and will cause premature curing of cyanoacrylate adhesives, while it becomes important to include oxygen in the reservoir of fasteners utilizing anaerobic adhesives.
After a reservoir cup is filled with the proper amount of adhesive, a piston is inserted in the open end to seal the interior. It has been found that a hydraulic lock may occur preventing insertion of the piston into the reservoir cup which prevents the piston from properly seating in the cup. Such lock can also prevent further displacement of the piston into the cup to expel the adhesive, or create a buildup of excessive pressure within the reservoir leading to a squirting out of the adhesive as the fastener is applied to a substrate to which it is to be attached.
Accordingly, modifications of both the reservoir and the fastener have been found desirable as well as the methods of charging the reservoir cup with adhesive and inserting the piston therein.